Tadpole-type amphiphilic dendrimers with bulky dendrons: Adsorption and aggregation properties

Tadpole-type amphiphilic dendrimers featuring a hexadecyl chain and two or three poly(amidoamine) dendrons (C 16 - m denG n , where m is the number of dendron scaffolds (2 or 3) and n is the dendron (den) generation (G) number (1, 2, 3, 4, or 5)) were synthesized using hexadecylamine or N -hexadecylethylenediamine as central scaffolds. These dendrimers were characterized by acid-base titration, surface tension, pyrene fluorescence, static light scattering (SLS), and small-angle neutron scattering (SANS), and showed clear breakpoints in their surface tension vs. concentration plots. This behavior was indicative of adsorption at the air/water interface and micelle formation in solution despite the bulky dendron structure (e.g., generations 3–5), contrasting the behavior of conventional surfactants. Contrary to our expectation, the C 16 - m denG n dendrimers could be densely packed at the air/water interface owing to enhanced hydrogen bonding between amide groups in the case of higher generation numbers. Furthermore, the above dendrimers formed spherical micelles in solution at a concentration of 5.00 mmol dm −3 (pH 9), regardless of the dendron generation number. As the generation number was increased to 4 for C 16 -2denG n and 3 for C 16 -3denG n , aggregates of spherical micelles were observed. The radius of gyration of C 16 - m denG n dendrimers was estimated as 2.0–2.5 nm, being almost independent of the hydrophilic dendron size.